The problems of Behçet's disease in Japan have been reviewed with particular emphasis on the ophthalmologic aspects: the historical background for the Japanese works, diagnostic critieria, epidemiology, some statistics, ocular symptomatology, ocular histopathology, etiology, pathophysiology, and treatment. Behçet's disease is the most frequent entity in endogenous uveitis in Japan. Patients are found throughout the country, and the prevalence rate averages seven to eight per 100,000 population: the rate is higher in the northern than in the southern districts. The diagnosis is made on the basis of a combination of clinical symptoms that are divided into the major and minor criteria symptoms. The major criteria comprise the ocular involvement, aphthous ulcers of the oral mucous membrane, genital ulcers, and skin lesions. These symptoms recur often as attacks and the disease follows a chronic course. The ocular involvement is found in 83% to 95% in males and 67% to 73% in females; the male to female ratio in the number of patients is 1.78. Both into the anterior segment type and the fundus and panophthalmic types. The anterior segment type shows serous iridocyclitis with the classic type of hypopyon appearing in about 12% of the attacks. This type is found in about 20%, more often in females than in males, and the visual prognosis is more favorable than in the fundus and panophthalmic types. In the latter two types, attacks of retinal angitis resulting in intensive retinal edema, yellowish-white exudate, and hemorrhages recur particularly in the macular region, and the visual prognosis is poor. More than 50% of male patients lose visual acuity to less than 0.1 in five years, but this is the case in only 10% of female patients. Consequently, Behçet's disease is the cause of blindness in about 12% of acquired blindness in adults. The ocular histopathology during the attack is characterized by severe angitis with intensive infiltration of neutrophil leucocytes largely in the uveal tract and the retina; the latter is severely affected and loss of visual cells and other neural elements results. The etiology of this disease still remains unknown but genetic predisposition is suggested since this disease is strongly linked with HL-A-B5. Environmental factors are also considered. Various abnormalities are found in the blood chemistry, blood cells (particularly in neutrophil leucocytes), immunologic mechanism, fibrinolytic and blood clotting system, and hormonal system. Chemotractic factors are found in the aqueous humor. These changes are particulary enhanced just before and during the ocular attacks. Systemic corticosteroids are deleterious to the visual prognosis, but cyclophosphamide and colchicine appear to suppress attacks and help patients maintain the visual acuity. However, these drugs are toxic, particulary to the reproductive organs, and the patients must be informed of this side effect and be allowed to make a decision before they are used.